Torsional motion of buildings during earthquakes. II. Inelastic response

1998 ◽  
Vol 25 (5) ◽  
pp. 917-934 ◽  
Author(s):  
J L Humar ◽  
P Kumar
Keyword(s):  
Building Code ◽  
Elastic Response ◽  
Earthquake Response ◽  
Torsional Motion ◽  
Inelastic Response ◽  
Torsional Response ◽  
Earthquake Motion ◽  
Building Models ◽  
Edge Based

In a previous study on the elastic torsional response of building models subjected to earthquake motion, it was shown that the current provisions of the National Building Code of Canada for design against torsion induced by earthquakes are quite conservative for the flexible edge of the building, but may be inadequate for the stiff edge. Based on the results of studies on the elastic response, a new set of design provisions was suggested. The present study deals with the inelastic torsional response of single- and multi-storey buildings designed according to the suggested provisions. Effects of both the natural and the accidental torsion are considered. It is shown that, given the complexity of inelastic response, particularly that of multistorey buildings, the suggested provisions can reasonably be used for the torsion design of single-storey buildings, as well as of multistorey buildings that are asymmetric in plan, but otherwise fairly regular.Key words: earthquake response, natural torsion, accidental torsion, inelastic torsional response, design for torsion.

Torsional motion of buildings during earthquakes. I. Elastic response

1998 ◽  
Vol 25 (5) ◽  
pp. 898-916 ◽  
Author(s):  
J L Humar ◽  
P Kumar
Keyword(s):  
Good Practice ◽  
The Other ◽  
Elastic Response ◽  
Earthquake Response ◽  
Torsional Motion ◽  
Torsional Response ◽  
A Value ◽  
Earthquake Motion ◽  
Building Models ◽  
Storey Building

Analytical studies are carried out on the elastic torsional response of single- and multi-storey building models subjected to earthquake motion. Effects of both the natural and accidental torsion are considered. The results of analysis are compared with the design provisions of the National Building Code of Canada (NBCC). It is shown that the NBCC provisions for the design of resisting elements on the flexible side are overly conservative. On the other hand, provisions for the design of elements on the stiff side are conservative in some situations and inadequate in others. Modifications to the design provisions are suggested which give design forces closer to the results obtained from a dynamic analysis, and are at the same time simpler than the existing provisions. It is shown that the ratio of the uncoupled torsional and translational frequencies is an important parameter governing the torsional response and it would be a good practice in design to achieve a value greater than 1 for this ratio.Key words: earthquake response, natural torsion, accidental torsion, elastic torsional response, design for torsion.

Design for forces induced by seismic torsion

2003 ◽  
Vol 30 (2) ◽  
pp. 328-337 ◽  
Author(s):  
JagMohan Humar ◽  
Soheil Yavari ◽  
Murat Saatcioglu
Keyword(s):  
Static Load ◽  
Building Code ◽  
Torsional Motion ◽  
Analysis Method ◽  
Torsional Response ◽  
Equivalent Static Load ◽  
Torsionally Flexible ◽  
Strength And Stiffness ◽  
Inertia Forces ◽  
Method Of Design

Eccentricities between the centres of rigidity and centres of mass in a building cause torsional motion during an earthquake. Seismic torsion leads to increased displacement at the extremes of the building and may cause distress in the lateral load-resisting elements located at the edges, particularly in buildings that are torsionally flexible. For an equivalent static load method of design against torsion, the 1995 National Building Code of Canada specifies values of the eccentricity of points through which the inertia forces of an earthquake should be applied. In general, the code requirements are quite conservative. They do not place any restriction on the torsional flexibility, however. New proposals for 2005 edition of the code which simplify the design eccentricity expressions and remove some of the unnecessary conservatism are described. The new proposals will require that a dynamic analysis method of design be used when the torsional flexibility of the building is large. Results of analytical studies, which show that the new proposals would lead to satisfactory design, are presented.Key words: torsional response to earthquake, natural torsion, accidental torsion, design for torsion, National Building Code of Canada, interdependence of strength and stiffness.

Dynamic response of buildings to ground rotational motion

1984 ◽  
Vol 11 (1) ◽  
pp. 48-56 ◽  
Author(s):  
A. M. Awad ◽  
J. L. Humar
Keyword(s):  
Dynamic Response ◽  
Rotational Motion ◽  
Translational Motion ◽  
Torsional Motion ◽  
Rotational Component ◽  
Torsional Response ◽  
Building Model ◽  
Earthquake Motion ◽  
Earthquake Force ◽  
Storey Building

Torsional motion in a building subjected to earthquake force is often attributed to an eccentricity between the centres of mass and resistance of the building. However, a more direct cause of torsional response is the presence of a rotational component in the earthquake motion. The effect of such a rotational motion on the response of both a symmetric and an unsymmetric single storey building model is studied. It is shown that the rotational component of excitation may have a very significant effect on the response, and that this effect may at times be more pronounced than the effect of torsion resulting from translational motion combined with plan eccentricity.

The effect of element strength assignment on the torsional response of stiffness-eccentric systems

2013 ◽  
Vol 40 (7) ◽  
pp. 655-662
Author(s):  
George K. Georgoussis
Keyword(s):  
Structural Design ◽  
Shear Force ◽  
Ground Motions ◽  
Building Structures ◽  
Centre Of Mass ◽  
Base Shear ◽  
Structural Behaviour ◽  
Torsional Response ◽  
Building Models ◽  
Storey Building

Building structures of low or medium height are usually designed with a pseudostatic approach using a base shear much lower than that predicted from an elastic spectrum. Given this shear force, the objective of this paper is to evaluate the effect of the element strength assignment (as determined by several building codes) on the torsional response of inelastic single-storey eccentric structures and to provide guidelines for minimizing this structural behaviour. It is demonstrated that the expected torque about the centre of mass (CM) may be, with equal probability, positive (counterclockwise) or negative (clockwise). This result means that the torsional strength should also be provided in equal terms in both rotational directions, and therefore the base shear and torque (BST) surface of a given system must be symmetrical (or approximately symmetrical). In stiffness-eccentric systems, appropriate BST surfaces may be obtained when a structural design is based on a pair of design eccentricities in a symmetrical order about CM, and this is shown in representative single-storey building models under characteristic ground motions.

Effects of Site Classification on Platform Value of Response Spectrum

2011 ◽  
Vol 378-379 ◽  
pp. 306-309
Author(s):  
Ping Li ◽  
Jing Shan Bo ◽  
Xiao Yun Guo ◽  
You Wei Sun ◽  
Yu Dong Zhang
Keyword(s):  
Ground Motion ◽  
Seismic Design ◽  
Wave Motion ◽  
Response Spectrum ◽  
Equivalent Linearization ◽  
Earthquake Response ◽  
Response Analysis ◽  
Site Classification ◽  
Earthquake Motion ◽  
Design Response Spectrum

Regarding the design response spectrum in the code for seismic design of buildings as target spectra，the 28 acceleration histories are formed artificially．They are used as the inputs ground motion in earthquake response analysis．Four site classifications profiles were selected or constructed from practical site profiles．With the use of 1-D equivalent linearization wave motion method that is wildly used at present in site seismic response analysis, the platform values of surface response spectrum for different profiles under different ground motion inputs were calculated．Different platform values of the response spectrum and relational expression which is seven input earthquake motion intensity and site classifications have been given by statistical analysis.

Design for seismic torsional forces

1984 ◽  
Vol 11 (2) ◽  
pp. 150-163 ◽  
Author(s):  
J. L. Humar
Keyword(s):  
Ground Motion ◽  
Analytical Study ◽  
Critical Evaluation ◽  
Building Code ◽  
Rotational Ground Motion ◽  
Building Model ◽  
Design Basis ◽  
Building Models ◽  
Adequate Design ◽  
Code Provisions

An analytical study of the responses of a single storey and a multistorey building model to a combined translational and rotational ground motion is presented. The models, which are assumed to be elastic, are eccentric about one plan direction but are symmetric about the perpendicular direction. The ground excitations are represented by idealized spectra.A critical evaluation is made of the torsion provisions of the National Building Code of Canada. It is shown that the code provisions, while not necessarily nonconservative, are somewhat difficult to apply for multistorey buildings. An alternative provision for design eccentricity is proposed. The forces obtained by the use of the proposed method are compared with the analytical results of single storey and multistorey building models and are shown to provide an adequate design basis.

Ground Motion Prediction Equation (“Attenuation Relationship”) for Inelastic Response Spectra

2010 ◽  
Vol 26 (1) ◽  
pp. 1-23 ◽  
Author(s):  
Yousef Bozorgnia ◽  
Mahmoud M. Hachem ◽  
Kenneth W. Campbell
Keyword(s):  
Ground Motion ◽  
Response Spectra ◽  
Prediction Equation ◽  
Elastic Response ◽  
Motion Prediction ◽  
Ground Motion Prediction Equation ◽  
Attenuation Relationship ◽  
Ground Motion Prediction ◽  
Inelastic Response ◽  
Local Soil

This paper presents the process and fundamental results of a comprehensive ground motion prediction equation (GMPE, or “attenuation” relationship) developed for inelastic response spectra. We used over 3,100 horizontal ground motions recorded in 64 earthquakes with moment magnitudes ranging from 4.3–7.9 and rupture distances ranging from 0.1–199 km. For each record, we computed inelastic spectra for ductility ranging from one (elastic response) to eight. Our GMPE correlates inelastic spectral ordinates to earthquake magnitude, site-to-source distance, fault mechanism, local soil properties, and basin effects. The developed GMPE is used in both deterministic and probabilistic hazard analyses to directly generate inelastic spectra. This is in contrast to developing “attenuation” relationships for elastic response spectra, carrying out a hazard analysis, and subsequently adopting approximate rules to derive inelastic response from elastic spectra.

Study of Dynamic Collapse of Single Layer Reticular Domes Subjected to Earthquake Motion and the Estimation of Statically Equivalent Seismic Forces

1997 ◽  
Vol 12 (3-4) ◽  
pp. 191-203 ◽  
Author(s):  
Shiro Kato ◽  
Takashi Ueki ◽  
Yoichi Mukaiyama
Keyword(s):  
Linear Response ◽  
Single Layer ◽  
Earthquake Response ◽  
Response Characteristics ◽  
High Rise ◽  
Earthquake Motion ◽  
Linear Buckling ◽  
Nonlinear Static ◽  
Dynamic Response Characteristics ◽  
Seismic Forces

The present paper investigates the dynamic response characteristics of single layer reticular domes subjected to horizontal earthquake motions from the following view points: (1) how to estimate the statically equivalent seismic forces applied to domes both for high rise and low rise; and (2) how to estimate the collapse accelerations under which the domes collapse dynamically. For these purposes, linear response analyses, linear buckling analyses, geometrically and materially nonlinear static analyses and geometrically and materially nonlinear earthquake response analyses are performed. Based on the results, the collapse accelerations are expressed as a function of the safety factor for domes under self weight. The expression for the collapse accelerations leads to an approximate measure by which structural designers may balance the static resistant capacity under self weight and the dynamic resistant capacity under earthquake motions.

Inelastic seismic response of concrete shear walls consideringP–delta effects

2001 ◽  
Vol 28 (4) ◽  
pp. 640-655 ◽  
Author(s):  
R Tremblay ◽  
P Léger ◽  
J Tu
Keyword(s):  
Plastic Hinge ◽  
Design Procedure ◽  
Building Code ◽  
Stability Factor ◽  
Dynamic Shear ◽  
Shear Forces ◽  
Inelastic Response ◽  
Higher Mode Effects ◽  
Mode Effects ◽  
Wall Structures

The inelastic response of a typical 12-storey ductile reinforced concrete flexural wall is examined under strong earthquake ground motions to determine the importance of P–delta effects and assess the seismic demand in shear and flexure. According to the stability factor approach of the National Building Code of Canada (NBCC) to account for P–delta effects, the flexural strength of the wall has to be increased by as much as 29%. However, the inelastic dynamic analyses indicate that P–delta effects on lateral deformations and curvature ductility demand are negligible for walls that meet the 2% NBCC interstorey drift requirement. The current NBCC stability factor approach to consider P–delta effects is thus overly conservative for shear wall structures, which respond significantly in their second and higher modes of vibration. The analyses also indicate that the magnitude and distribution of shear forces and bending moments in the wall are different from those obtained using the NBCC static design procedure. Plastic hinges can occur above the base of the wall, although the probable moment resistance diagram exceeds the assumed moment envelope after plastic hinge formation at the base. Dynamic amplification of shear forces due to higher mode effects was also observed, which must be accounted for in design. Dynamic shear amplification factors proposed for wall structures in the commentary to the current standard for design of concrete structures in Canada compared well with the results of this study.Key words: seismic, flexural wall, P–delta effects, stability coefficient, inelastic response, National Building Code of Canada, dynamic shear force amplification, higher mode effects.

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